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To study the working mechanism and failure causes of semi-sealed ram blowout preventer, the full-size simulation model of semi-sealed ram is established in this paper. The failure analysis and strength evaluation of semi-sealing ram are carried out. The simulation of the blowout preventer ram in the process of well sealing under different well pressure impacts is studied, and the stress and strain distribution law is found out, and the causes of rubber core seal failure are analyzed. The analysis results show that the groove root of the ram body just enters the yield deformation when the oil cylinder pressure exceeds a certain value, and the maximum von Mises stress occurs at the groove root of the ram body, and the stress concentration and fluid impact pressure lead to the premature fracture failure of the ram. It is also found that the stress concentration in the contact area between the rubber core and the upper end of the ram is the most obvious, indicating that the upper part of the rubber core is severely deformed due to extrusion because of well pressure, which will cause fatigue damage to the rubber core over time. Finally, the extrusion behavior of the contact part between the ram and the drill pipe is highly consistent with the shape of the high-stress zone in the simulation analysis, which proves that the simulation result is reliable. [ABSTRACT FROM AUTHOR]

• The optimum constitutive relation data of rubber core were obtained. • Obtain real calculation results through the simulation calculation of rubber core. • The secondary optimization design of the rubber core structure is studied. • The superiority of the improved structure is verified by the test and application. In order to reduce the failure of the spherical blowout preventer, the basic calculation formula of the sealing geometric parameters of the spherical blowout preventer are deduced combined with the existing structure and working principle of the spherical blowout preventer in this paper. Based on the test data of four constitutive relationships of rubber core material, the constitutive relationship of rubber core material is obtained by optimizing the four kinds of test data. And this paper studies the deformation law, stress distribution and sealing performance of the rubber core by using finite element software, and finds out the internal of failure causes of the spherical rubber core. The calculation results show that the stress concentration is obvious at the bottom of the rubber core, which is one of the main reasons for the falling off of the rubber rings. The stress values of the neck and back of the support rib are high, which is easy to cause the support rib to bend and break along the neck and back. The indoor test shows that the designed rubber core structure meets the pressure test requirements, and the appearance of the annular rubber core is intact after used in the field. It shows that the optimized structure is helpful to improve the service life of the spherical rubber core. [ABSTRACT FROM AUTHOR]

In this paper, microstructures and mechanical properties of the fractured drive shaft are investigated by visual inspection, metallographic analysis, scanning electron microscopy, and tensile and impact tests. The composition, structure and mechanical properties of the drive shaft materials are tested to meet the standards. The fracture surface is mainly characterized by dimples and a small amount of quasi-cleavage by microscopic analysis, which indicates that the fracture surface is dominated by ductile fracture. At the bottom of the sample pit, there are a large number of grey inclusions, which are turned to be iron oxides through EDS spectrum analysis. So, the existence of a large number of iron oxide inclusions in the metal will inevitably have a serious impact on the performance of drive shaft. The finite element analysis shows that the stress on the cylindrical surface of the external thread near the shoulder will gradually increase greatly and the rupture risk will increase with the increase of the torque and that it will also fails due to the relatively high stress on the root of the first tooth of thread. The maximum stress near the thread shoulder is close to the yield limit of the material when the borehole curvature is larger and the bending load will lead to stress concentration on the optical axis section at the shoulder, which will affect the safety of drive shaft. Because there are a large number of inclusions in raw materials and the conditions in the well are complex, the carrying capacity of drive shaft decreases and fracture of the drive shaft is finally caused. The maximum stress value of the improved drive shaft is lower than that before the improvement through the comparative analysis. It shows that the safety factor and service life of the drive shaft can be improved by the improved design. • Did the testing of composition and mechanical properties about material of shaft. • The area had good toughness through scanning electron microscopy of sample. • Carried out the three-dimension simulation of M119 × 4–6g. • The largest stress was at the regions of actual fracture site. • Mechanical strength analysis and structural improvement of drive shaft. [ABSTRACT FROM AUTHOR]

Failure analysis of crossing pipelines in the operation process after the completion of construction was investigated. Dent and collapse are the common failure modes of crossing pipelines in bad geological strata. The deformation processes of dent behaviour and collapse behaviour of crossing pipelines were simulated. The results show that high stress distribution extends along the axial and circumferential directions under the boulder load, and the maximum equivalent plastic strain appears at the centre of the dent. The collapse process of the crossing pipeline can be divided into six phases. The cross-section changes from an oval shape to a “gourd” shape and then to an “8” shape as the external load increases. Before buckling appears, the decrease in the cross-section area of the crossing pipeline is small. However, the cross-section area increases as the surrounding soil pressure increases after buckling appears. When the cross-section shape reaches the “8”, the decrease in the cross-section area reaches a maximum value of 88.1%. To reduce the failure probability and improve the service life of the crossing pipeline, a protective device was designed for preventing damage. For the protective device, the dent rate of the protective pipeline decreases as the annulus pressure increases under the action of boulders. However, the dent rate of the crossing pipeline increases as the annulus pressure increases. Under the same stratum movement, the deformation of the crossing pipeline with the protective device is smaller than without the protective device. Therefore, the protective device can effectively protect the crossing pipeline and prevent a collapse accident. The protective device can be effectively used on any parts of the crossing pipeline in different locations due to its simple structure and convenient installation in bad geological strata. [ABSTRACT FROM AUTHOR]